Java Interview Questions

masterstroke · 23-12-2009, 05:54 AM

Q) What is explicit casting?

Quote:

Explicit casting in the process in which the complier are specifically informed to about transforming the object.

Example

long i = 700.20;

int j = (int) i; //Explicit casting

masterstroke · 23-12-2009, 05:56 AM

Access specifiers are keywords that determine the type of access to the member of a class. These keywords are for allowing privileges to parts of a program such as functions and variables. These are:

Public : accessible to all classes
Protected : accessible to the classes within the same package and any subclasses.
Private : accessible only to the class to which they belong
Default : accessible to the class to which they belong and to subclasses within the same package

masterstroke · 23-12-2009, 05:57 AM

Object class is the superclass of every class.

masterstroke · 23-12-2009, 05:58 AM

The 8 primitive types are byte, char, short, int, long, float, double, and boolean.

masterstroke · 23-12-2009, 06:00 AM

A static variable is associated with the class as a whole rather than with specific instances of a class. Each object will share a common copy of the static variables i.e. there is only one copy per class, no matter how many objects are created from it.

Class variables or static variables are declared with the static keyword in a class. These are declared outside a class and stored in static memory. Class variables are mostly used for constants.

Static variables are always called by the class name.

This variable is created when the program starts and gets destroyed when the programs stops.

The scope of the class variable is same an instance variable. Its initial value is same as instance variable and gets a default value when its not initialized corresponding to the data type.

Similarly, a static method is a method that belongs to the class rather than any object of the class and doesn’t apply to an object or even require that any objects of the class have been instantiated.

Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object.

A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final.

However, you can’t override a static method with a non-static method. In other words, you can’t change a static method into an instance method in a subclass.

Non-static variables take on unique values with each object instance.

masterstroke · 23-12-2009, 06:02 AM

If an expression involving the boolean & operator is evaluated, both operands are evaluated, whereas the && operator is a short cut operator.

When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. If the first operand evaluates to false, the evaluation of the second operand is skipped.

masterstroke · 23-12-2009, 06:02 AM

Program compiles and runs properly.

masterstroke · 23-12-2009, 06:03 AM

In declaration we only mention the type of the variable and its name without initializing it.

Defining means declaration + initialization.

E.g. String str; is just a declaration

while String str = new String (”abhi”); Or String str = “abhi”; are both definitions.

masterstroke · 23-12-2009, 06:04 AM

In Java the arguments (primitives and objects) are always passed by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object.

masterstroke · 23-12-2009, 06:05 AM

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. Objects allow procedures to be encapsulated with their data to reduce potential interference. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.

23-12-2009, 05:56 AM	#2
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What are different types of Java access modifiers? Access specifiers are keywords that determine the type of access to the member of a class. These keywords are for allowing privileges to parts of a program such as functions and variables. These are: Public : accessible to all classes Protected : accessible to the classes within the same package and any subclasses. Private : accessible only to the class to which they belong Default : accessible to the class to which they belong and to subclasses within the same package

23-12-2009, 05:57 AM	#3
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	Which class is the superclass of every class? Object class is the superclass of every class.

23-12-2009, 05:58 AM	#4
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	Which are the 8 primitive Java types. The 8 primitive types are byte, char, short, int, long, float, double, and boolean.

23-12-2009, 06:00 AM	#5
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What are the differences between static and non-static variables? A static variable is associated with the class as a whole rather than with specific instances of a class. Each object will share a common copy of the static variables i.e. there is only one copy per class, no matter how many objects are created from it. Class variables or static variables are declared with the static keyword in a class. These are declared outside a class and stored in static memory. Class variables are mostly used for constants. Static variables are always called by the class name. This variable is created when the program starts and gets destroyed when the programs stops. The scope of the class variable is same an instance variable. Its initial value is same as instance variable and gets a default value when its not initialized corresponding to the data type. Similarly, a static method is a method that belongs to the class rather than any object of the class and doesn’t apply to an object or even require that any objects of the class have been instantiated. Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can’t override a static method with a non-static method. In other words, you can’t change a static method into an instance method in a subclass. Non-static variables take on unique values with each object instance.

23-12-2009, 06:02 AM	#6
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What is the difference between the boolean & operator and the && operator? If an expression involving the boolean & operator is evaluated, both operands are evaluated, whereas the && operator is a short cut operator. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. If the first operand evaluates to false, the evaluation of the second operand is skipped.

23-12-2009, 06:02 AM	#7
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What if I write static public void instead of public static void? Program compiles and runs properly.

23-12-2009, 06:03 AM	#8
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What is the difference between declaring a variable and defining a variable? In declaration we only mention the type of the variable and its name without initializing it. Defining means declaration + initialization. E.g. String str; is just a declaration while String str = new String (”abhi”); Or String str = “abhi”; are both definitions.

23-12-2009, 06:04 AM	#9
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	What type of parameter passing does Java support? In Java the arguments (primitives and objects) are always passed by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object.

23-12-2009, 06:05 AM	#10
masterstroke Member Join Date: Dec 2009 Posts: 33 Rep Power: 0	Explain the Encapsulation principle. Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. Objects allow procedures to be encapsulated with their data to reduce potential interference. One way to think about encapsulation is as a protective wrapper that prevents code and data from being arbitrarily accessed by other code defined outside the wrapper.